1. Field of the Invention
The present invention relates to an electronic ignition control apparatus, or a knock control apparatus for an internal-combustion engine, which ensures the detection of a knock phenomenon without restriction to the characteristic of the engine, such as the driving state thereof.
2. Description of the Related Art
Control systems for detecting and suppressing a knock phenomenon occurring in an internal-combustion engine, include a fuel control system, an ignition timing control system and a pressure gate control system. The ignition timing control system, the most frequently used system of these control systems will now be explained.
The following describes a knock control (ignition control) apparatus that utilizes the conventional ignition timing control system for an internal-combustion engine as shown in FIG. 1. Such in ignition timing control type knock control apparatus is known, for instance, from U.S. Pat. No. 4,377,999. The ignition timing control system includes an acceleration sensor 1 for sensing an acceleration of a mechanical vibration of an internal-combustion engine 30, a frequency filter 2 for passing that signal component of the output signal from the acceleration sensor 1 which has a high frequency sensible to knocking; an analog gate 3 for cutting off noise contained in the filtered signal of the frequency filter 2 which may interfere with the detection of such a knock phenomenon, and a gate timing controller 4 for controlling the operation of the analog gate 3 in accordance with the occurrence of the noise.
The output of the frequency filter 2 that has passed through the analog gate 3 is supplied to a noise level detector 5 and a comparator 6 as well.
This noise level detector 5 detects the level of noise caused by other mechanical vibrations of the internal-combustion engine 30 than the knock phenomenon and sends it to the comparator 6. This comparator 6 compares the output of the analog gate 3 with the output of the noise level detector 5 to produce a knock detecting pulse and sends this pulse to an integrator 7.
The integrator 7 integrates the knock detecting pulse from the comparator 6 and produces an integrated voltage according to the knocking intensity. The integrated voltage is supplied to a phase shifter 8, which shifts the phase of a reference ignition signal in accordance with the output of the integrator 7.
Reference numeral 9 is a revolution signal generator that produces the above-described reference ignition (revolution) signal according to a preset ignition advance angle characteristic. The output of the revolution signal generator 9 is wave-shaped in a waveform shaper 10 which, at the same time, executes the duty angle controlling for energization of an ignition coil 12.
A switching circuit 11 is responsive to the output signal of the phase shifter 8 to interrupt the power supply to an ignition coil 12. This coil 12 generates an ignition pulse which is supplied, to a spark plug (not shown).
FIG. 2 illustrates the frequency characteristics of the output signal, or vibration signal of the acceleration sensor 1. In FIG. 2, numerals 80 and 82 indicate the frequency characteristics in the absence of a knocking phenomenon and in the presence of a knocking phenomenon, respectively.
The output signal of the acceleration sensor 1 contains a knock signal (i.e., the signal generated during a knock phenomenon), other mechanical noise components originating from the vibration of the internal-combustion engine 30 and various noise components passing through signal transfer paths, for example, ignition noise. From the comparison of the frequency curve 80 with the curve 82 of FIG. 2, it is readily understood that the knock signal has a specific frequency distribution characteristic.
Although the difference in the frequency distribution characteristic between these two curves depends on the type of the internal-combustion engine in use and also where the acceleration sensor 1 is mounted, one is clearly distinguished from the other with regard to whether or not the knocking phenomenon occurs in the engine.
In this respect, therefore, filtering the frequency component of the knock signal suppresses the noise of the other frequency components thereby to effectively detect the knock signal.
FIGS. 3 and 4 illustrate the waveforms of individual circuit components of FIG. 1 in one-to-one correspondence. FIG. 3 is for the operation mode where no knocking is caused in the internal-combustion engine 30, whereas FIG. 4 is for the operation mode where knocking is caused in the engine 30.
Referring now to FIGS. 3 and 4, the operation of the conventional knock control apparatus for the internal-combustion engine 30 as shown in FIG. 1 will be explained. When the internal-combustion engine 30 is rotated, an ignition signal is produced as a reference ignition signal from the revolution signal generator 9 in accordance wit the preset ignition timing characteristic. This ignition signal is wave-shaped into a pulse having a desired duty angle by the waveform shaper 10, and this pulse drives switching circuit 11 through the phase shifter 8 to interrupt the power supply to the ignition coil 12. The ignition voltage that is induced across the ignition coil 12 by the interruption of the coil energization ignites the spark plug and operates the engine 30.
The engine 30 in operation causes mechanical vibrations, which are all detected by the acceleration sensor 1.
Without knocking caused in the internal-combustion engine 30, no knocking-dependent mechanical vibrations would occur, but there would be other mechanical vibrations which could cause the output signal of the acceleration sensor 1 to have mechanical noise as shown in FIG. 3A and ignition noise passing through the signal transfer paths at each ignition timing (FIRING).
The mechanical noise component of this output signal, when filtered by the frequency filter 2, is significantly suppressed as shown in FIG. 3B. However, since the ignition noise component is stronger than the mechanical noise component, it is not reduced so much after passing the frequency filter 2.
Such an output waveform is likely to cause the ignition noise to be mistaken as the knocking signal, so that the analog gate 3 is opened for some period of time from the ignition timing by the output (see FIG. 3C) of the gate timing controller 4 that is triggered by the output of the phase shifter 8. With the gate 3 opened, the ignition noise from the frequency filter 2 is inhibited from going to the comparator 6. As a consequence, the output of the analog gate 3 contains only a low-leveled mechanical noise as indicated by 84 in FIG. 3D.
In response to a change in the peak of the output signal of the analog gate 3, the noise level detector 5 produces a DC voltage whose level is slightly higher than the peak of the mechanical noise (see 85 in FIG. 3D). In this case, the noise level detector 5 has a characteristic which is responsive to a relatively gentle change in the peak of the output signal of the analog gate 3 that is caused by the peak of ordinary mechanical noise.
Since the output 85 of the noise level detector 5 is greater than the average peak value of the output signal 84 of the analog gate 3 as shown in FIG. 3D, the comparator 6 for comparing these output with each other would have no output as shown in FIG. 3E. As a result, all the noise signals except the knocking signal can be removed.
Under these circumstances, therefore, the output voltage of the integrator 7 remains null as shown in FIG. 3F and the phase angle of the phase shifter 8 becomes zero as well. The phase angle here means the phase difference between the output (FIG. 3G) of the waveform shaper 10 and the output (FIG. 3H) of the phase shifter 8.
The switching phase of the switching circuit 11 that is driven by the output, or ignition signal (FIG. 3G) of the phase shifter 8, i.e., the intermittent phase of the energization of the ignition coil 12, is the same as the phase of the reference ignition signal (FIG. 3G) from the waveform shaper 10. Consequently, the ignition timing becomes the reference ignition timing.
Now with knocking caused in the internal-combustion engine 30, the output of the acceleration sensor 1 contains knocking-dependent noise at around a point of time with some delay from the ignition timing as shown in FIG. 4A, and the signal passing through the frequency filter 2 and the analog gate 3 is a high knock signal superimposed on mechanical noise as indicated by 88 in FIG. 4D.
Of the signals passing through the analog gate 3, the knocking signal has a sharp rising so that the level of the output voltage 89 from the noise level detector 5 (which is substantially identical to the voltage 85 in FIG. 3D) has a slow response to the knock signal.
Consequently, the inputs of the comparator 6 have the waveforms 88 and 89 in FIG. 4D, respectively, so that the comparator's output has a pulse as shown in FIG. 4E.
The integrator 7 integrates this pulse and produces the integrated voltage as shown in FIG. 4F. Then, in accordance with the output of the integrator 7, the phase shifter 8 retards the phase of the output signal (FIG. 4G) of the waveform shaper 10, or the phase of the reference ignition signal. Consequently, the output of the phase shifter 8 lags by .DELTA.t (delta "t") from the phase of the reference ignition signal from the waveform shaper 10, and drives the switching circuit 11 with its phase as shown in FIG. 4H. This delays the ignition timing thereby to suppress knocking. Then, the driving states of the internal-combustion engine 30 shown in FIGS. 3 and 4 are repeated to achieve the optimum ignition timing control.
Depending on the driving characteristics of the engine 30, the level ratio of the two inputs of the comparator 6 cannot be set to the proper ratio value to perform the desired knocking phenomenon detection. In other words, the ability of the comparator 6 to discriminate the knocking signal from mechanical noise with the detected noise signals 85 and 89 of the noise level detector 5 as the threshold levels, would be undesirably deteriorated.
The driving characteristics of the engine 30 implies the voltage characteristic of two input signals to the comparator 6 with respect to the rotation of the engine: the first input signal to the comparator being the waveform 84 in FIG. 3D or waveform 88 in FIG. 4D (each being the output of the analog gate 3) and the other input signal being the waveform 85 in FIG. 3D or waveform 89 in FIG. 4D (the output of the noise level detector 5). That is, the engine's driving characteristic is determined by the vibration characteristic of the engine 30 and the detection characteristic of the acceleration sensor 2.
According to the above conventional knock, or ignition control apparatus, in consideration of the characteristic to detect the knocking phenomena caused in different rotation regions of the internal-combustion engine and the system design plan, the knocking detection characteristic should be set at the sacrifice of some of the knocking control ability.
With the above conventional drawwbacks, it is an object of the present invention to provide a knock, or ignition control apparatus for an internal-combustion engine, which is capable of directly controlling the output voltage characteristic of a noise level detector in accordance with the driving state of the engine.